1. Field of the Invention
This invention relates to methods for manufacturing of metal cans, and in particular to the manufacture of a reclosable can having a threaded neck portion for receiving a threaded closure to seal contents in the container. The threaded neck portion on a can of this invention is attached to a cylindrical can body and has threads integrally formed therein or on a threaded sleeve on the neck portion. The threaded neck portion is secured on the top of the can by double seaming, adhesive or other permanent attachment means. The threaded portion is adapted to receive a plastic or metal closure.
2. Description of the Prior Art
It is known to form drawn, or drawn and ironed, cans from aluminum and steel for use in packaging of beer, soft drinks, oil, and other liquids and also for use as aerosol containers for a variety of products. Most metal cans for beer and beverages are adapted to be closed with relatively flat lids or ends which are secured on the cans by double seaming or the like. The lids may have tear strips formed in them and have pull tabs attached to the tear strips to facilitate forming pouring openings in the lids. It is also known to provide cans with cone top ends on them as disclosed in U.S. Pat. Nos. 4,262,815; 4,574,975; 4,793,510 and 4,911,323. It is further known to provide an easy opening container with a reduced diameter cylindrical portion on it and angular spaced thread segments on the cylindrical portion as disclosed in U.S. Pat. No. 3,844,443. That patent also discloses a method for forming such a container which includes one or more forming operations such as drawing and ironing operations.
U.S. Pat. No. 5,293,765 discloses a method and apparatus for manufacturing threaded aluminum containers by deep drawing, deep drawing and additional stretching, or extrusion, and rolling threads in a necked-in portion on the end of the container. The threads are formed by positioning first and second thread rolling tools adjacent the inside and outside surfaces of the container and rotatably moving the tools against the surfaces. The patent states that the container wall thickness must be maximally 20% of the pitch of the thread used for the container.
Threaded aluminum containers have typically been made from relatively thick metal, i.e., at least 0.020 inch thick. The aluminum has typically been relatively soft in order to permit the forming of the threads in such neck.
An improved method is desired for forming a can having a threaded neck portion from thin gauge hard temper metal which is preferably an aluminum alloy. Additionally, an improved metal can is desired which has a threaded neck on it for securement of a closure on the can. A method is desired for forming threaded cans from hard temper aluminum alloy sheet material having a thickness of about 0.007-0.015 inch. A threaded aluminum can is desired which is capable of holding positive pressure in the can in the range of 40 to 110 psi when closed with a threaded closure.